1. Field of the Invention
This invention relates to a vacuum type circuit breaker of the type using the difference between the internal pressure of a vacuum switch tube and atmospheric pressure as a contact force for a movable electrode against a fixed electrode, and more particularly to an operating mechanism adapted to make the closing of the switch impossible upon occurrence of vacuum loss in the vacuum switch tube.
2. Description of the Prior Art
Japanese Patent Publication No. 15225/1976 discloses an example of a device of this type. The disclosed vacuum type circuit breaker, which is adapted to use the difference between the internal pressure of the vacuum switch tube and atmospheric pressure as a contact pressure for the movable electrode of the vacuum switch tube against the fixed electrode thereof, comprises an electromagnet for imparting a closing operative force to the movable electrode, and a return spring for separating the movable electrode from the fixed electrode, the arrangement being such that when vacuum loss occurs in the vacuum switch tube, the equilibrium between the opening force of the return spring and the difference between the internal pressure of the vacuum switch tube and atmospheric pressure is upset, so that even if a closing instruction is given to energize the electromagnet, the closing of the switch is prevented because of the upset of equilibrium among the attraction of the electromagnet, the opening force of the return spring and the difference between the internal pressure of the vacuum switch tube and atmospheric pressure.
However, this conventional vacuum type circuit breaker, because of its arrangement described above, has not only the disadvantage of requiring a power source of large capacity for operating the electromagnet but also the disadvantage of being very unstable in that variations in the operating power source voltage cause variations in the closing speed or upset the equilibrium of forces to the extent that the closing of the switch is no longer possible. Further, upon occurrence of an operating power source failure, low speed closing must be manually effected. Thus, it also has a drawback from the standpoint of safety.
U.S. Pat. No. 4,152,562 issued May 1, 1979 and entitled "Driving Mechanism For Switching Apparatus With Pressure Contacts" discloses the relation between an electrode-opening spring and atmospheric pressure in a spring-operated vacuum type circuit breaker which is different from the solenoid-operated type described above. Similarly, in "Developments In Distribution Switchgear" in Conference Publication Number 168, J. Parry describes the relation between an electrode opening spring and atmospheric pressure in a vacuum type circuit breaker. These two prior techniques disclose that it is necessary for the opening spring to overcome the force applied to the contacts of the vacuum type circuit breaker by atmospheric pressure.